1. Field of the Invention
The present invention relates to an electric power converter and more specifically, it relates to an electric power converter to be installed in an electric vehicle or a hybrid vehicle.
2. Description of Related Art
An electric vehicle or a hybrid vehicle is equipped with an electric motor to be used as a motive power source for the vehicle and normally includes an electric power converter such as an inverter, that is engaged in operation in order to control the electric power supplied to the motor.
Such an electric power converter system will typically comprise a power module that includes power semiconductors such as insulated gate bipolar transistors (IGBTs), a drive circuit that drives the power module, a control circuit that controls the power module and the drive circuit, and a capacitor engaged in operation to smooth an electric current. These electronic components are vulnerable to high temperatures and thus need to be cooled.
While a large-capacity electric power converter, which generates a great deal of heat, is often equipped with a cooler that cools the electronic components by circulating cooling water, an electric power converter may include an alternative cooling system, normally referred to as a “Boiling Refrigerant Type Cooling Device” achieved by filling a sealed container with a coolant so as to ensure that the coolant assumes a state of vapor-liquid two-phase equilibrium within the sealed container.
The cooling device used to cool the power semiconductors, at which heat is generated in particularly large quantities among the components of the electric power converter described above, especially is required to assure a high level of performance. Japanese Laid Open Patent Publication No. 2000-277962 and Japanese Laid Open Patent Publication No. H7-176662, for instance, each disclose a cooling structure for a semiconductor element, which features a boiling refrigerant type cooling device.
In addition, the components of the electric power converter other than the power semiconductors, such as the drive circuit, the control circuit and the capacitor, each of which is an exothermic component or a component vulnerable to high temperatures, may need to be individually cooled, as does the power module, depending upon the size of the electric power converter or the installation density. WO2000/017994, for instance, discloses a cooling structure for a control element in the control circuit, which supports the control element by thermally contacting a casing via a heat-conducting means.
The cooler adopting any of the technologies in the related art described above is utilized in an electric power converter as a cooling means for cooling power semiconductors such as IGBTs, as described in, for instance, Japanese Laid Open Patent Publication No. 2000-277962 mentioned earlier.
However, since the electric power converter includes numerous other exothermic components or components vulnerable to high temperatures, such as the drive circuit, the control circuit and the current smoothing capacitor, in addition to the power semiconductors, a heat management, i.e., a cooling control similar to that used for the power semiconductors, must be applied to these electronic components as well.
There is a particularly urgent need for further miniaturization of the electric power converter in an electric vehicle or a hybrid vehicle in which comfortable passenger space must be assured. Since the overall exothermic density is bound to increase when the electric power converter is miniaturized, a more compact electric power converter will require a cooling means for an increasing number of components disposed within the converter, to the point where a cooling means is applied to practically every component.
While WO 2000/017994 mentioned earlier, for instance, discloses a design concept whereby an optimal cooling structure is devised for each individual component, this approach is bound to cause an increase in the cost for cooling design and cooling components as the number of cooling target components rises, which, in turn, is bound to degrade the product economics.